Tube conduction systems containing several tube elements which are connected to each other by simple insertion are very frequently employed in medicine. A typical example of this is the connection between a Y-coupler and a tube of a medicinal oxygen-supply system such as used, for instance, in operations together with an anesthesia machine.
The connections can be made rapidly as a result of the insertion. The tube elements of such a connection can, however, become loose. For instance, in the case of the connection between the tube and the Y-coupler of an oxygen-supply system this can lead to serious accidents resulting in death, particularly in the case of a patient who is being completely supplied with oxygen and, in particular, also when active respiration is not possible, due, for instance, to the administration of muscle relaxants.
In addition to this, the tube elements used in medical tube connections are frequently low cost articles which are used only once and therefore are manufactured with relatively large tolerances with respect of their cross-sectional dimensions, so that the danger of disconnection cannot be excluded because of these tolerances.
A system for monitoring the connection between a coupler and a tube of a medicinal oxygen-supply system is known (U.S. Pat. No. 3,595,228). The known system consists essentially of a circuit having an oscillator. By means of an electric connecting line, which extends over ohmic contacts between the tube and the coupler, the oscillator is grounded on the body of the patient, whereby swinging of the oscillator is prevented. If the connection between the tube and the coupler comes loose and the connecting line is thereby interrupted, the oscillator is activated to generate an audio frequency to a loudspeaker of the system.
This known system has the disadvantage that it requires a connecting line on the body of the patient. This is undesirable for reasons of safety. Furthermore, there is the danger that, in the known system, the generation of an audio signal will be suppressed even if, after a loosening of the connection between the coupler and the tube, the coupler should accidently happen to come against the patient so that the oscillator is still grounded on the patient via the probe line, even though the connection to be monitored has been actually interrupted.
An alarm device is also known by which the presence of an infusion liquid in an infusion system is monitored (U.S. Pat. No. 3,942,526). In the known device, a float is provided in a space traversed by the infusion liquid which float moves downward in said space in the absence of infusion liquid and, by means of a permanent magnet, actuates a sensor which is formed by a reed contact. A monitoring system for medicinal tube connections is not conceived in this case.